Technical Field
This technology relates to ballistic resistant composite articles having improved backface deformation resistance as well as superior ballistic penetration resistance. Particularly, this technology relates to hybrid, multi-panel ballistic resistant articles that are especially useful for the fabrication of body armor.
Description of the Related Art
Ballistic resistant articles such as bullet resistant vests, helmets, vehicle panels and structural members of military equipment are typically made from composite armor comprising high strength fibers. High strength fibers conventionally used to fabricate composite armor include polyethylene fibers, aramid fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon fibers, glass fibers and the like. For some applications, the fibers are formed into woven or knitted fabrics. For other applications, the fibers are coated with a polymeric binder material and formed into non-woven fabrics.
Various ballistic resistant constructions are known that are useful for the formation of hard or soft body armor articles such as helmets and vests. For example, U.S. Pat. Nos. 4,403,012, 4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402, 4,748,064, 5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, all of which are incorporated herein by reference, describe ballistic resistant composites which include high strength fibers made from materials such as extended chain ultra-high molecular weight polyethylene (UHMW PE). These composites display varying degrees of ballistic resistance to high speed projectiles such as bullets, shells, shrapnel and the like.
The two primary measures of anti-ballistic performance of composite armor are ballistic penetration resistance and blunt trauma (“trauma”) resistance. A common characterization of ballistic penetration resistance is the V50 velocity, which is the experimentally derived, statistically calculated impact velocity at which a projectile is expected to completely penetrate armor 50% of the time and be completely stopped by the armor 50% of the time. For composites of equal areal density (i.e. the weight of the composite armor divided by the surface area) the higher the V50 the better the penetration resistance of the composite. In this regard, it is known that the V50 ballistic performance of fibrous composite armor is directly related to the strength of the constituent fibers of the composite.
Whether or not a high speed projectile penetrates armor, when the projectile engages the armor the impact also deflects the body armor at the area of impact, potentially causing significant non-penetrating, blunt trauma injuries. The measure of the depth of deflection of body armor due to a bullet impact is known as backface signature (“BFS”), also known in the art as backface deformation or trauma signature. Potentially resulting blunt trauma injuries may be as deadly to an individual as if the bullet had fully penetrated the armor and entered the body. This is especially consequential in the context of helmet armor, where the transient protrusion caused by a stopped bullet can still cross the plane of the skull underneath the helmet and cause debilitating or fatal brain damage. Accordingly, there is a need in the art for ballistic resistant composites having both superior V50 ballistic performance as well as low backface signature.
This disclosure provides a solution to this need. Particularly, it has been unexpectedly found that body armor having excellent ballistic penetration resistance performance and backface signature performance can be achieved at a lower cost by combining multiple different sections of materials. The sections are arranged into a gradient wherein the outermost, strike-face section of the article is formed from fibers having the highest tenacity of the article, and the outermost section on the opposite side of the article will be formed from the lowest tenacity fibers of the article or from no fibers at all. In this regard, each section of the composite article performs a different function. The first, outermost strike-face section of fibrous plies functions to break open the metal casing of a bullet, such as a 9 mm Full Metal Jacket (FMJ) bullet which comprises a lead core portion covered by a copper casing (jacket). Breaking open of the casing will thereby expose the lead core. The second section of fibrous plies will then deform any remaining portion of the casing material as well as the bullet core material and also reduce the velocity of the deformed parts and any projectile fragments. The third section will then distribute the remaining kinetic energy of the bullet over a large area and thus reduce the trauma energy transmitted to the user of the armor. Together, the different sections of material provide excellent ballistic penetration resistance and trauma resistance.